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The Digestive System Mouth (oral cavity) Tongue Esophagus Liver Gallbladder Small intestine Duodenum Jejunum Ileum Anus Parotid gland Sublingual gland Submandibular gland Salivary glands Pharynx Stomach Pancreas (Spleen) Transverse colon Descending colon Ascending colon Cecum Sigmoid colon Rectum Vermiform appendix Anal canal Large intestine Nerve Artery Vein Mesentery Intrinsic nerve plexuses • Myenteric nerve plexus • Submucosal nerve plexus Glands in submucosa Mucosa • Epithelium • Lamina propria • Muscularis mucosae Submucosa Muscularis externa • Longitudinal muscle • Circular muscle Serosa • Epithelium • Connective tissue Lumen Gland in mucosa Lymphatic Mucosa-associated Duct of gland outside vessel lymphoid tissue alimentary canal From mouth (a) Peristalsis: Adjacent segments of alimentary tract organs alternately contract and relax, which moves food along the tract distally. (b) Segmentation: Nonadjacent segments of alimentary tract organs alternately contract and relax, moving the food forward then backward. Food mixing and slow food propulsion occurs. Soft palate Palatoglossal arch Hard palate Uvula Oral cavity Palatine tonsil Tongue Oropharynx Lingual tonsil Epiglottis Hyoid bone Laryngopharynx Esophagus Trachea Sagittal section of the oral cavity and pharynx Crown Neck Enamel Dentin Dentinal tubules Pulp cavity (contains blood vessels and nerves) Gingiva (gum) Cementum Root Root canal Periodontal ligament Apical foramen Bone Gingivae (gums) Palatine raphe Hard palate Soft palate Uvula Palatine tonsil Upper lip Superior labial frenulum Palatoglossal arch Palatopharyngeal arch Posterior wall of oropharynx Tongue Sublingual fold with openings of sublingual ducts Vestibule Lower lip Lingual frenulum Opening of submandibular duct Gingivae (gums) Inferior labial frenulum Bolus of food Tongue Uvula Pharynx Bolus Epiglottis Epiglottis Glottis Trachea Bolus Esophagus 1 Upper esophageal sphincter is contracted. During the buccal phase, the tongue presses against the hard palate, forcing the food bolus into the oropharynx where the involuntary phase begins. Relaxed muscles 2 The uvula and larynx rise to prevent food from entering respiratory passageways. The tongue blocks off the mouth. The upper esophageal sphincter relaxes, allowing food to enter the esophagus. 4 Food is moved through the esophagus to the stomach by peristalsis. Circular muscles contract Bolus of food 3 The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after entry. Relaxed muscles 5 The gastroesophageal sphincter opens, and food enters the stomach. Longitudinal muscles contract Gastroesophageal sphincter closed Gastroesophageal sphincter opens Stomach Bolus of food Tongue Pharynx Epiglottis Glottis Trachea 1 Upper esophageal sphincter is contracted. During the buccal phase, the tongue presses against the hard palate, forcing the food bolus into the oropharynx where the involuntary phase begins. Uvula Bolus Epiglottis Esophagus 2 The uvula and larynx rise to prevent food from entering respiratory passageways. The tongue blocks off the mouth. The upper esophageal sphincter relaxes, allowing food to enter the esophagus. Bolus 3 The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after entry. Relaxed muscles Circular muscles contract 4 Food is moved through the esophagus to the stomach by peristalsis. Bolus of food Longitudinal muscles contract Gastroesophageal sphincter closed Stomach Relaxed muscles 5 The gastroesophageal sphincter opens, and food enters the stomach. Gastroesophageal sphincter opens Cardia Fundus Esophagus Muscularis externa • Longitudinal layer • Circular layer • Oblique layer Lesser curvature Serosa Body Lumen Rugae of mucosa Greater curvature Duodenum Pyloric Pyloric canal antrum Pyloric sphincter (valve) at pylorus Liver Gallbladder Lesser omentum Stomach Duodenum Transverse colon Small intestine Cecum Urinary bladder Interlobular veins (to hepatic vein) Central vein Sinusoids Bile canaliculi Plates of hepatocytes Bile duct (receives bile from bile canaliculi) Fenestrated lining (endothelial cells) of sinusoids Portal vein Hepatic macrophages in sinusoid walls Bile duct Portal venule Portal arteriole Portal triad (c) Figure 23.25c Right and left hepatic ducts of liver Cystic duct Common hepatic duct Bile duct and sphincter Accessory pancreatic duct Mucosa with folds Gallbladder Major duodenal papilla Hepatopancreatic ampulla and sphincter Tail of pancreas Pancreas Jejunum Duodenum Main pancreatic duct and sphincter Head of pancreas Left colic (splenic) flexure Right colic (hepatic) flexure Transverse mesocolon Transverse colon Epiploic appendages Superior mesenteric artery Descending colon Haustrum Ascending colon Cut edge of mesentery IIeum Teniae coli IIeocecal valve Sigmoid colon Cecum Vermiform appendix Rectum Anal canal External anal sphincter Glycolysis Krebs cycle Electron transport chain and oxidative phosphorylation Carbon atom Phosphate Glucose Phase 1 Sugar Activation Glucose is activated by 2 ADP phosphorylation and converted to fructose-1, Fructose-1,66-bisphosphate bisphosphate Glycolysis Krebs cycle Electron transport chain and oxidative phosphorylation Carbon atom Phosphate Fructose-1,6bisphosphate Phase 2 Sugar Cleavage Fructose-1, 6-bisphosphate is cleaved into two 3-carbon Dihydroxyacetone fragments phosphate Glyceraldehyde 3-phosphate Glycolysis Krebs cycle Electron transport chain and oxidative phosphorylation Carbon atom Phosphate Dihydroxyacetone phosphate Glyceraldehyde 3-phosphate Phase 3 Sugar oxidation and formation 2 NAD+ of ATP 4 ADP The 3-carbon fragments are oxidized 2 NADH+H+ (by removal of hydrogen) and 4 ATP molecules are formed 2 Pyruvic acid 2 NADH+H+ 2 NAD+ 2 Lactic acid To Krebs cycle (aerobic pathway) Glycolysis Krebs cycle Electron transport chain and oxidative phosphorylation Cytosol Pyruvic acid from glycolysis Transitional phase Carbon atom Inorganic phosphate Coenzyme A Mitochondrion (matrix) NAD+ CO2 NADH+H+ Acetyl CoA Oxaloacetic acid NADH+H+ (pickup molecule) Citric acid (initial reactant) NAD+ Malic acid Isocitric acid NAD+ Krebs cycle CO2 NADH+H+ -Ketoglutaric acid Fumaric acid CO2 FADH2 Succinic acid FAD GTP ADP Succinyl-CoA GDP + NAD+ NADH+H+ Chemical energy (high-energy electrons) Chemical energy Glycolysis Glucose Cytosol Krebs cycle Pyruvic acid Mitochondrial cristae Via substrate-level phosphorylation 1 During glycolysis, each glucose molecule is broken down into two molecules of pyruvic acid in the cytosol. Electron transport chain and oxidative phosphorylation Mitochondrion 2 The pyruvic acid then enters the mitochondrial matrix, where the Krebs cycle decomposes it to CO2. During glycolysis and the Krebs cycle, small amounts of ATP are formed by substratelevel phosphorylation. Via oxidative phosphorylation 3 Energy-rich electrons picked up by coenzymes are transferred to the electron transport chain, built into the cristae membrane. The electron transport chain carries out oxidative phosphorylation, which accounts for most of the ATP generated by cellular respiration. Lipids Lipase Glycerol Fatty acids H2O Glyceraldehyde phosphate (a glycolysis intermediate) b Oxidation in the mitochondria Glycolysis Pyruvic acid Acetyl CoA Krebs cycle Coenzyme A NAD+ NADH + H+ FAD FADH2 Cleavage enzyme snips off 2C fragments Glycolysis Glucose Stored fats in adipose tissue Dietary fats Glycerol Triglycerides (neutral fats) Lipogenesis Fatty acids Ketone bodies Ketogenesis (in liver) Glyceraldehyde phosphate Pyruvic acid Certain amino acids Acetyl CoA CO2 + H2O + Steroids Bile salts Catabolic reactions Anabolic reactions Cholesterol Krebs cycle Electron transport Proteins Carbohydrates Fats Proteins Glycogen Triglycerides (neutral fats) Glucose Amino acids Glucose-6-phosphate Keto acids Glycerol and fatty acids Glyceraldehyde phosphate Pyruvic acid Lactic acid NH3 Acetyl CoA Ketone bodies Urea Excreted in urine Krebs cycle Food Pyramid